Abstract
OBJECTIVE: To assess the relationship between the changing Accountable Care Organizations-ACO workforce and ACOs' shared savings earnings and quality performance. DATA SOURCES: Medicare Shared Savings Program-MSSP provider-level research identifiable files, performance year financial and quality report public use files, and National Physician Compare data (2013-2021). STUDY SETTING AND DESIGN: We characterized 865 MSSPs, separately pre- (2013-2019) and post-pandemic (2020-2021) according to the percentage of primary care physicians (PCPs), non-physicians, specialists, and other specialty, financial risk model, assigned Medicare beneficiary demographics, clinical risk factors, and provider supply by specialty within the MSSP's primary service state, (total and per-capita) shared savings earnings/losses owed and quality score. Longitudinal ordinary least-squares regressions with random effects were estimated to assess the association between MSSP provider specialty mix and annual (1) per-capita shared savings/losses and (2) quality score, controlling for risk model, beneficiary characteristics, provider supply, and year factors. We also compared outcomes across MSSPs, 32 Pioneers and 62 Next Generation-NGACOs. PRINCIPAL FINDINGS: PCPs represented 33.9% of MSSP's workforce, on average. Higher percentages of PCPs and non-physicians were associated with higher per-capita earned shared savings and quality scores among MSSPs. A 1-percentage-point (ppt) increase in PCPs and non-physicians was associated with higher per-capita shared savings of $2.25 (p < 0.01) and $1.82 (p = 0.03), respectively, pre-COVID, and $2.73 (p < 0.01) and $1.81 (p = 0.14) post-COVID. We estimated increases in quality scores among MSSPs of ~0.1 ppt with a 1 ppt increase in PCPs, non-physicians, and specialists only pre-pandemic. No statistically significant relationships were estimated between provider specialty mix and performance measures in Pioneers and NGACOs. CONCLUSIONS: Higher percentages of PCPs and non-physicians were associated with higher per-capita shared savings earnings and quality scores among MSSPs. As new federal initiatives continue to unfold, value-based payment models increasing incentives for primary care should be monitored to determine their ability to further improve care efficiency.